Magnetic Innovation — An idea for Sucker Rod Pumps

Jay Jani
Jay Jani
Aug 24, 2017 · 8 min read

Sucker rod pump or beam pump (SRP) was the first type of artificial lift to be introduced to the oil field. It is also the most widely used in terms of the number of installations worldwide, accounting for about 80% of total artificial lift completions. The low cost, mechanical simplicity and the ease with which efficient operation can be achieved makes rod pumps suitable for low volume operations that are quite common in ONGC and other mature fields in India.

This type of artificial lift utilizes a positive displacement pump that is inserted or set in the tubing near the bottom of the well. The pump plunger is connected to surface by a long rod string, called sucker rods, and operated by a beam unit at surface. Each upstroke of the beam unit lifts the oil above the pump’s plunger.

However, the frequent reciprocating movement of sucker rods in the barrel pump creates repetitive mechanical problems. In ONGC’s Mehsana Asset, in 2010, over 25% wells on SRP required a well servicing job within a year. Moreover upto 40% of all workover jobs comprise of Repair of SRP (RSRP) and the oil gain from these jobs is the least amongst all kinds of workover jobs. This aspect presents a significant challenge in handling SRPs because it is the major artificial lift form but results in frequent expenditure.

Most failures associated with the sucker rod lift method can be attributed to one of three primary downhole components — subsurface pump, sucker rod string or tubing string. Most of the time, all these failures require deployment of a workover rig, pull out of complete string and then reinstallation of the string.

Mechanical failures account for a large percentage of the total number of all rod string failures. Mechanical damage to the rod string causes a stress raiser which ultimately will cause the sucker rods or coupling to fail. One of the most common reason for this kind of failure is the fatigue caused by wear and tear of either sucker rod string or tubing string. A variety of methods such as installation of guides, rollers, tubing anchors, etc. have been tried and implemented successfully in the oilfield. Yet, the failure rate is significant. And approximately, 50% of the SRP failures are due to tubing leakage and sucker rod string failure.

To resolve this key challenge, the below proposal aims to reduce the mechanical interference of sucker rod string with tubing string by the induction of magnetic strips on sucker rods and use of diamagnetic material inside tubings. A magnetic strip can be attached at key locations, where normally guides or rollers are coupled, and these strips can create a repulsive force within the tubing composed of diamagnetic material like copper and ensure centralized alignment of the rod string, thereby reducing mechanical wear and tear of various components.

Magnetic model

A Sucker Rod Pump (SRP) provides mechanical energy to lift oil from bottom hole to surface. It is efficient, simple, and easy for field people to operate. It can pump a well down to very low pressure in order to maximize oil production rate. It is applicable to slim holes, multiple completions, deviated wells, and high-temperature and viscous oil wells. The major disadvantages of SRPs include excessive friction in crooked/deviated holes, solid-sensitive problems, low-efficiency in gassy wells, and limited depth due to rod capacity.

In the conventional system, installation of SRP involves first run-in of a standing valve with a pump barrel on a tubing string. Once, run upto the desired depth, this standing valve is tested at a requisite pressure to ensure the integrity of the complete tubing string. Consequently, a plunger consisting of travelling valve is run on a sucker rod string that moves inside the tubing string. When the plunger reaches inside the pump barrel, the run-in of sucker string is completed and final adjustment is carried out at the surface to ensure the requisite buildup of pressure (normally, about 50 kg/cm2) at the surface.

The pump is installed in the tubing string below the dynamic liquid level. It consists of a working
barrel and liner, standing valve (SV), and traveling valve (TV) at the bottom of the plunger, which is connected to sucker rods. As the plunger is moved downward by the sucker rod string, the TV is open, which allows the fluid to pass through the valve, which lets the plunger move to a position just above the SV. During this downward motion of the plunger, the SV is closed; thus, the fluid is forced to pass through the TV. When the plunger is at the bottom of the stroke and starts an upward stroke, the TV closes and the SV opens. As upward motion continues, the fluid in the well below the SV is drawn into the volume above the SV (fluid passing through the open SV). The fluid continues to fill the volume above the SV until the plunger reaches the top of its stroke.

During this complete cycle, the sucker rod string moves inside tubing and at times comes in contact with the inner body of tubing because of misalignment caused by the wellbore inclination. Majority of wells in which SRP is installed are not vertical. That means sucker rod string needs some centralizing component to keep it aligned to the centre of the tubing string. Most common approach to centralize is the use of rod rollers or soft moulded guides. These rollers or guides have outer diameter equal to the drift diameter of the tubing string and thus when installed onto the rod string, keep the string aligned to the centre. These guides or rollers are sequentially coupled to a set of sucker rods and are normally placed at depths which have maximum inclination such that the string avoids contact with the tubing. However, the use of guides or rollers has not mitigated the problem of wear and tear in SRPs to a very large extent.

Often, the weaker of the two, i.e. the roller and tubing, wears out and causes string failure. Numerous metallurgical compositions have been tried with guides and these attempts have prolonged life of SRP without failure but still the problem persists.

To overcome this challenge, this proposal aims to use magnetic strips that can be fixated on the body of sucker rods sequentially such that the interference of rod string and tubing string is completely eliminated and results in smooth, and continuous movement of sucker rods with negligible friction.

A magnetic strip of thickness upto 0.5 inches can be used for this purpose. In wells with viscous oil, many a times a chemical injection line is lowered along with the tubing string to inject chemicals to reduce the viscosity of oil. This line is attached to the tubing strip by use of mechanical fastener strips at two to three locations per tubing. The magnetic strip proposed is analogous to that mechanism and can be similarly attached in this case but this time to the rod string. The magnet should be prepared and fabricated in such a manner, that it repels the inner body of tubing string all the time. For this purpose, a superconductor or a diamagnetic material inside the tubing needs to be placed. Because the normal steel used in tubings will create an attractive force. Hence, the magnet needs to be fabricated in a manner so that it does not get attracted by steel but does repel the copper that can be placed at suitable locations inside tubing. Alternatively, all tubings manufactured of copper can be run in if the commercial feasibility permits. When such strip, run on a sucker rod, enters the tubing string, the magnetic strip will cause a repulsive force inside the tubing that will result in central alignment of the complete rod string. The magnetic strip will create an equal radial force and will ensure proper central alignment. In this way, the friction between the rod and tubing string will be eliminated, resulting in reduced fatigue, corrosion, and mechanical failure of SRP.

To carry out this proposal, a miniature model of rod and magnet strip should be prepared and passed through a hollow tube. Prior to that, first the effect and force of magnet must be studied. The fabrication of magnet can be empirically designed from the miniature experiment. It is essential that the magnetic force should be kept at the optimum level. A high magnetic force can destabilize the rod as it moves inside the tubing whereas a low magnetic force will make the alignment ineffective. The position of magnetic strips on the sucker rods can be determined in the same way as that of rollers is determined based on the inclination angle calculation of the wellbore. Also, there needs to be no change in the rod string sequence and it can be run as per the API 11.

The inner side of the magnetic strip should be fabricated in such a manner that it creates an attractive force and thus remains attached to the rod body. Whereas the outer side should create a radial repulsive force that repels the tubing body. The specifications of sucker rod, tubing and magnetic strip must be determined after studying the magnetic properties of variety of metals and alloys.

Such a design will reduce fatigue and corrosion. As a result, the need for frequent workover jobs will be reduced, saving servicing expenditure as well as cost of non-productive well time.

Utility in India

Almost 80% of wells dependent on artificial lift in India use SRP as primary mechanism. An operational SRP involves only a minor electricity cost and thus is very efficient and inexpensive compared to other artificial life systems such as the gas lift, PCP, and ESP. Moreover, it doesn’t need additional infrastructure development as is the case with gas lift system and thus, SRP can be implemented easily and quickly to remote wells.

And yet it remains a fact that the number of SRP wells requiring frequent servicing is growing. The reason being more number of inclined and deviated wells, corrosive environment, gas interference, and deterioration of old tubings with the increasing age of the well. Today, SRP account for about 40% of all workover jobs and require significant rig time as well as cost. On many occasions, unavailability of rig causes the wells to remain shut in for a large duration and can also lead wells to cease. Hence, there is a growing need to overcome this challenge of SRP failures and this proposal directly relates to the challenges faced by Indian companies in most of their mature fields.

A large part of ONGC’s existing oil fields were discovered and commissioned in 1980s and the recovery rate for most wells is in the range of 30–35%. Due to aging and maturity of these fields, artificial lift installation is a necessity. But, the low operational volume of these wells require the maintenance cost associated with these wells to be kept at bare minimum. This proposal aims to reduce the workover requirement of such wells and ensure more rig-free time for the wells. This proposal can help ONGC achieve one of the key aims of PP2030 by accomplishing better brownfield management of wells.

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Jay Jani

Written by

Jay Jani

Jay is a Production Engineer working in India's National Oil Company - ONGC. Loves energy, environment, technology, books, travelling and public speaking.

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